Previous studies have suggested that (1) sensory-motor representation can be activated during the comprehension of words or sentences, (2) the activation depends on the participants' past experiences of interaction with real external objects or actual situations, and (3) past experiences can facilitate the comprehension of words or sentences. What kinds of interaction will facilitate the comprehension, however, still remain uncovered. In order to examine this, we conducted an experiment in which thirty-three Japanese university students were randomly assigned to one of the following three groups: (a) participants who were asked to enact the sentences, which included at least one English indefinite pronoun, and observe other participants' enactment --the enactment group, (b) participants who were asked to observe the same enactments as shown by group (a)--the observation group, and (c) participants who were not asked to either enact or observe--the control group. In order to examine what kinds of interaction will facilitate the comprehension of the concept of English indefinite pronouns, we set a grammar test designed to assess students' understanding of the concept before and after the treatment. The grammar test revealed that the enactment group outperformed not only the control group but also the observation group. This result suggests that the experience of enacting sentences can facilitate participants' comprehension of the concept of word meaning--English indefinite pronouns in this study--and that the mere observation of enactments cannot facilitate this comprehension. The reason of the facilitation was discussed.
